1. Field of the Invention
The invention relates to a mixture of oligomeric phenazinium compounds and to a method of preparing such a mixture. The invention further relates to an acidic bath for electrolytically depositing a copper deposit containing the oligomeric phenazinium compounds as well as to a method of electrolytically depositing a copper deposit using said bath. The mixture of the invention may be utilized as a constituent in copper plating baths to more specifically form highly bright level deposits of copper in order to produce decorative surfaces. The mixture may moreover be utilized as a constituent in copper plating baths for selectively and completely filling blind microvias in printed circuit boards with copper. The mixture may further also be utilized as a constituent in copper plating baths for depositing copper onto semiconductor substrate surfaces provided with recesses (trenches and vias) during the manufacturing of integrated circuits, with the entire semiconductor substrate surface being uniformly coated with copper.
2. Brief Description of the Related Art
For depositing bright copper layers instead of a crystalline matte deposit, organic additives are usually added in small quantities to most of the acidic copper electrolytes. In this approach, an additive compound or a combination of several additive compounds such as polyethylene glycols, thioureas and their derivatives, thio hydantoin, thio carbamic acid esters as well as thio phosphoric acid esters is often added. Nowadays however, the additives mentioned are no longer significant, due to the fact that the quality of the thus obtained copper layers meets by no means today's requirements. The thus obtained coatings are either too brittle or exhibit poor brightness and insufficient levelling.
The utilization of certain safranines and of the derivatives thereof for producing bright copper layers has long been known, said safranines being used, in accordance with DE-PS 947 656, as the only additive, e.g., dimethyl safranine azo dimethyl aniline, diethyl safranine azo dimethyl aniline, Janus grey and safranine azo naphthol. It is moreover known to use said compounds in combination with other additives as well.
DE-AS 1 004 880 suggests the combination of diethyl tolusafranine azo dimethyl aniline, diethyl tolusafranine azo phenol, tolusafranine azo naphthol or dimethyl tolusafranine azo dimethyl aniline or of phenosafranine, tolusafranine, fuchsia, amethyst violet, mauveine, diethyl tolusafranine or dimethyl tolusafranine with thiourea and thiourea derivatives for depositing bright and level copper coatings. Patent Abstract of Japan corresponding to JP 60-056086 A relates to the combination of a phenazine dyestuff with mono- or disulfides such as (3-sodium-sulfopropyl)disulfide and bis-(3-sodium sulfoethyl)disulfide and polyethers for depositing highly bright, level, ductile copper layers. The suggestions made in DE-PS 947 656, DE-AS 1 004 880 and in Patent Abstract of Japan corresponding to JP 60-056086 A however result in copper coatings having unsatisfactory properties.
Further, the utilization of a thiourea-formaldehyde condensate as an additive to an acid copper plating bath has been described: DE-AS 1 152 863 describes pre-condensates of thiourea-formaldehyde being employed as the only leveller used in the bath. The basic brighteners contained in the described baths are compounds of the dithio carbamic acid-type derivatives. DE-AS 1 165 962 describes the use of pre-condensation products consisting of thiourea, formaldehyde and of a compound having at least two NH2 groups in an acidic bath for producing levelling copper coatings. The bath further contains basic brighteners.
DE-AS 1 218 247 discloses an acid electrolytic copper bath for producing highly bright, level copper coatings containing compounds that are hardly soluble in water and are comprised in the molecule of thiocarbonyl groups and aryl or aralkyl residues in a ratio of 1:1, said two groups being separated by hetero atoms that are either bonded to one another or form components of a ring system. These are for example aromatic N-monosubstitution products of thiosemicarbazide, further thiosemicarbazones of aromatic aldehydes, derivatives of thiocarbohydrazide, heterocyclic compounds having a thiocarbonyl group, thiuram mono- and polysulfides, dixanthogen mono- and polysulfides and hydrazine dithio carbonamide. These compounds may be used together with derivatives of sulfones and sulfoxides of the formula RR′N—CS—S—(CH2)n—SOx—R″.
Although the additives disclosed in DE-AS 1 152 863, DE-AS 1 165 962 and DE-AS 1 218 247 also permit to achieve bright copper surfaces, they fall short of today's requirements in practice because of their poor levelling qualities.
Moreover, polyalkylene imines having organic thio compounds have become known: DE-AS 1 246 347 discloses that one or several straight-chained or branched polyalkylene imines or the functional derivatives thereof are advantageous for producing bright, levelling and decoratively attractive copper coatings, with brightness being also achievable over a widened current density range. The functional derivatives more specifically mentioned are the salts of the polyalkylene imines and the products of their reaction with carbon dioxide, esters of carbonic acid, alkyl halogenides or fatty acids. These substances can be utilized in the bath together with other current brighteners and/or wetting agents.
Further, DE-AS 1 521 062 suggests bath compositions containing an organic sulfide that contains at least one sulfonic acid group as well as, mixed thereto or chemically bonded, a polyether that contains at least three, preferably six, oxygen atoms and is free of aliphatic hydrocarbon chains with more than six C-atoms. These baths permit deposition of smooth, bright and ductile copper layers. Preferred polyethers mentioned are 1,3-dioxolane polymerisates having a molecular weight of at least 296, preferably of about 5000. Phenazine dye-stuffs may also be utilized in combination with the bath additives mentioned, for example diethyl phenosafranine azo dimethyl aniline, dimethyl phenosafranine azo dimethyl aniline, diethyl phenosafranine azo phenol and dimethyl azo-(2-hydroxy-4-ethylamino-5-methyl)-benzene. The phenazine dyestuffs permit high levelling and a wide range of bright deposits.
With the copper electrolytes described in DE-AS 1 246 347 and DE-AS 1 521 062 it is not possible to apply a sufficiently high cathodic current density, though. Furthermore, the deposited copper surfaces can only be nickel-plated after having been subjected to an intermediate treatment.
Further, U.S. Pat. No. 4,551,212 discloses the use of a combination of Janus Green B or Janus Black R with Safranine T for depositing copper layers that are machinable in the micrometer range. The properties of these layers are optimized with regard to grain size and hardness. In addition to the phenazine dyestuffs mentioned, the bath may further contain a wetting agent as well as stress relieving agents such as bis-(3-sulfopropyl disulfide)disodium salt.
Moreover, the use of hydroxylated and halogenated safranine dyestuffs has been described in Patent Abstracts of Japan corresponding to JP 60-056086 A.
Like the other documents mentioned herein above, the additives disclosed in U.S. Pat. No. 4,551,212 and in Patent Abstracts of Japan corresponding to JP 60-056086 A only yield results showing poor brilliance and levelling.
DE-AS 20 28 803 and DE-AS 2 039 831 describe for the first time the use of polymeric phenazinium compounds having the general chemical formula <A>:
wherein R1, R2, R3, R4, R5, R6, R7, R8 and R9 are the same or different and are hydrogen, lower alkyl or possibly methyl-, ethyl-, methoxy- or ethoxy-substituted aryl and R5 and R8 further represent mono- or polymeric phenazinium cations, A is an acid residue and n is an integer of from 2 to 100. According to DE-AS 20 39 831, the starting substance for producing these compounds is a sulfuric acid amine such as 2-methyl-3-amino-6-dimethyl-amino-9-phenyl-phenazonium sulfate. Said amine is diazoted with sulfuric acid at −5° C. using nitrosyl sulfuric acid and nitrous acid. The reaction solution is heated to 20° C. after the nitrous acid has been destroyed. Then, the reaction mixture is neutralized with a base.
In principle, deposition of bright and level copper coatings using these compounds in an acid copper plating electrolyte is possible. However, they lead to very unstable results of the copper plating operation.
Therefore the basic object of the present invention is to circumvent the above drawbacks of the known copper baths.